Wire is unwound from a spool in many industrial manufacturing operations. Thus, for example, in the manufacture of steel belted radial tires, a plurality of wires 10 are drawn off from an array 12 of spools 14 supported on support frames 16 of an unwinding machine 18 as shown in FIG. 1. The wires 10 drawn from the spools 14 are then transferred to a calender for combination with rubber prior to a vulcanizing process (not shown).
During the drawing of the wires 10 from the array 12 of spools 14 shown in FIG. 1, it is desirable to control the tension applied in the wires 10, with the degree of tension depending in part upon the gauge of the wire being drawn. Thus, for example, in the manufacture of steel belted radial tiers for small cars, tension upwards of 0.1836 Newtons (i.e., "1.8 Kg") is desirable. However, in the manufacture of earth moving vehicular tires utilizing 3/8 in. diameter wire, tension upwards of 0.9180 Newtons (i.e., "9 Kg") is desirable.
A conventional method utilizes a magnetic chuck 20 as shown in FIG. 2 for the coupling of a spool 14 to a brake drum 22 of an unwinding machine 18 as shown in FIG. 1. During the unwinding process, selective braking of the brake drum 22 results in the application of the desired tension in the wire 10 that is drawn from the spool 14.
The conventional magnetic chuck 20 shown in FIG. 2 includes a magnet 24 disposed within a disc-like housing 26 including a lip 28 having a continuous planar surface 30 generally transverse to an axis 32 of a spindle 34 upon which it is rotatably supported. The spool 14 includes opposed identical ends 36 each having a plurality of radial ribs 38 formed in an end surface 40 for strengthening of the end 36 of the spool 14. A circular recess 42 is also defined by the end 36 of the spool 14 having a generally planar, annular surface 44 surrounding an axial passage 46 that extends through the center of the spool 14. The spool 14 is rotatably supported on the spindle 34 by extension of the spindle 34 through this passage 46.
The magnetic chuck 20 is secured to the brake drum 22 by conventional fasteners 48. The magnet 24 itself is adhered to a base 50 of the housing 26 using an adhesive. The lip 28 of the housing 26 extends axially away from the base 50 to surround the magnet 24. The magnet 24 magnetizes the continuous planar surface 30 of the lip 28.
The spool 14 is secured to the magnetic chuck 20 by magnetic engagement between the planar surface 30 of the lip 28 and the annular planar surface 44 of the recess 42 formed in the end 36 of the spool 14.
The arrangement of FIG. 2 performs well in the manufacture of steel belted radial tires in which the tension in the wires does not exceed approximately 0.1836 Newtons ("1.8 Kg"). However, once this upper limit is exceeded, the spool 14 retained simply through magnetic attraction against the planar surface 30 begins to slip thereon. Consequently, tension in the range of 0.9180 Newtons ("9 Kg")cannot be achieved using this conventional arrangement.
A known solution for achieving the higher desired tension includes the provision of a pin on the brake drum which extends within a bore of the spool for locking engagement therewith (not shown), whereby the spool would be physically precluded from rotating relative to the brake drum without first severing or bending of the locking pin. While such an arrangement is effective in achieving the desired tension, play between the pin and the bore in the spool leads to clanking and other undesirable noise during rotation of the spool in unwinding of the wire. Moreover, when a large plurality of spools simultaneously are being unwound as shown in FIG. 1, the noise becomes so great that ear protection must be worn by an operator attending to the unwinding machine.
Another disadvantage to this arrangement is that in the loading of a new spool of wire onto a spindle of the support frame, the bore in the side of the spool must be aligned with the locking pin disposed on the side of the brake drum for proper positioning of the spool on the spindle. While this may not be exceptionally tedious for the loading of a single spool, this task is impractical with a large array of spools as shown in FIG. 1.
Yet a third disadvantage to this arrangement is that during rotation of the spool on the spindle, the spindle tends to move away from the brake drum off of the locking pin and, consequently, an operator must constantly monitor the array of spools to insure that each is properly maintained in position on its spindle.
In view of the above conventional arrangements for unwinding wire from spools, it is clear that a need exists for an improved apparatus and method by which higher levels of tension easily exceeding 0.1836 Newtons ("1.8 Kg")can be achieved without encountering the foregoing disadvantages.